Effects of gait-related imagery and mirror visual feedback on cortical activation during robot-assisted gait training

Robot-aided gait training is expected to facilitate the recovery of lower limb functions in spinal cord injury (SCI) patients. This study determined whether gait-related imagery and visual feedback affects a cortical activation pattern during robot-aided gait of healthy subjects and SCI patients. Five healthy volunteers and four patients with chronic SCI (two completely paraplegic and two partially quadriplegic) participated in this study. We measured the cortical activation of the motor area during robot-aided gait by a near-infrared spectroscopic imaging system. After a 60 s resting stage, each subject walked on the treadmill with robotic assistance (GAR: Gait-Assistance Robot) for 1 min. The subjects performed actual and imaginary movements of their lower extremities in several ways: active assisted movement, passive movement, imaginary leg movement without actual movement, imagined leg movement with passive movement, and active assisted movement with mirror visual feedback. All gait patterns except passive movement showed cortical activation in the healthy subjects and partially quadriplegic SCI patients. The cortical activation of gait-related motor imagery was higher in the partially quadriplegic SCI patients compared with the healthy subjects. For the completely paraplegic SCI patients, it was difficult to induce cortical activation during the robot-assisted gait; however, only the mirror visual feedback effectively induced cortical activation. Our results indicate that partially quadriplegic SCI patients have not lost the motor imagery of their lower extremities. Motor imagery is an effective means to evoke cortical activation of the motor area during robot-aided gait training in such cases. Chronic completely paraplegic SCI patients could not induce cortical activation during robot-aided gait. Visual feedback is considered important for inducing cortical activation of the motor area during a robot-aided gait.